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This chapter deals with Geomorphic process,exogenic,endogenic
processes,diastrophism,volcanism,weathering,types of weathering
mechnical(unloading ,expansion,temperature change expansion
freezing thawing frost wedging salt weathering ), chemical
(solution, carnonation,hydration oxidation and
reduction),biological (plants, animals man).biological activity and
weathering, special effects of weathering, significance of
weathering, mass movement,slow movement, rapid movementland slide,
erosion , deposition, soilformtion, process of soil formation soil
forming factors, parent material, topography, climate, biological
activity, time.
1. Why earth is uneven? Due to internal and external forces
earth is changing its surface conditions. The earth crust is always
dynamic It moves vertically and horizontally The differences in the
internal forces making the surface uneven Wearing down of relief
features is called gradation. The endogenic forces always elevate
parrts of the earths surface and hence the exogenic processes fail
to even out the relief variations of the surface of the earth.
Variations remain as long as there is difference between endogenic
and exogenic forces. The surface of the earth is sensitive. Human
being is using the surface intensively and extensively. GEOMORPHIC
PROCESSES The endogenic and exogenic forces cause physical stress
and chemical actions on the earth material and bring the changes in
the configuration of the earth surface is called GEOMORPHIC
PROCESSES Diastrophism and volcanism are endogenic processes
Weathering, Masswasting,Erosion & Deposition Are Exogenic
Processes Any Exogenic Element Of Nature Capable Of Acquiring And
Transporting Earth Materials Can Be Called A Geomorphic Agent. They
Become Mobile When There Is Gradient The Erosional Agents Are
1.Running Water ,2. Moving Ice, 3.Wind, 4.Underground Water
,5.Waves A process is a force applied on earth materials affecting
the same
An agent is a mobile medium which removes transports and
deposits earth materials.
Gravity also causes directional forces activating downslope
movements of matter
Waves and tides are inderect movements of the earth caused by
gravitation
With out gravity and gradient there is no mobility for erosional
agents as a result there is no erosion transportation, and
deposition on the earth surface.
All the movements on/in the earth are due to gravitation and
gradient.from higher level to lower level and high pressure to low
pressure areas
ENDOGENIC PROCESS: the energy generating from with in the earth
is the main force behind the endogenic geomorphic processes.
The energy genarated due to 1. Radioactivity 2.Rotational Force
3.Tidal Friction 4.Primordial Heat From The Origin Of The
Earth.
Diastrophism And Volvanism Are Due To Geothermal Grdients And
Heat Flow From Within The Earth.
Crustal Thickness,Strength, Action Of Endogenic Forces Are Due
To Variations In Geothermal Gradients And Heat Flow Are Uneven.
DIASTROPHISM : All process that move elevate or duild up
portions of the erths crust come under DIASTROPHISM
THEY ARE TWO TYPES
CHAPTER -6 GEOMORPHIC PROCESSES
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1.OROGENIC PROCESSES : mountain building through folding
2.EPEROGENIC PROCESS: uplifting large part of earth crust 3.EARTH
QUAKES
4.PLATE TECTONICS: involve horizontal movements
DIFFERENCE BETWEEN OROGENY AND EPEROGENY
VOLCANISM: Movement of molten rock towards the earths surface
and also formation of many intrusive and extrusive volcanic forms.
Volcanism: it is the process in which volcanoes takes place
Volcanoes are the land forms formed due to volcanic process
EXOGENIC PROCESSES: They derive their energy from atmosphere
determined by the prime source The sun and also gradients created
by the tectonic factors. Gravitational force create gradient
towards down slope direction. Force applied per unit area is called
STRESS. Stress can be produced in a sold body pushing or pulling
This includes deformation. Forces acting along the faces of earth
materials are shear stresses .(seperating forces). It is this
stress that breaks rocks and other earth materials.the shear stress
result in angular displacement/slippage. Besides gravitational
stress there is molecular stress which is caused by temperature
change, crustallisation and melting .chemical processes normally
lead to loosening of bonds between grains , dissolving of soluble
minerals or cementing materials. The basic reason for weathering,
mass movement erosion and deposition is the development of stress
in the earth materials. Since there are different climatic regions
there is variation in the exogenic process from region to region.
Temperature and precipitation are the two major elements that
control various processes. All the exogenic process are covered
under general term DENUDATION. The word denude means uncover.
Weathering , masswasting erosion and transportation are
included in denudation.
DENUDATIONAL PROCESSES AND THEIR Driving Forces
In
OROGENY EPEROGENY
Crust is severely damaged Mountain building process Folding and
faulting Cause tension and comprssion
simple deformation continental formation upliftment of
landmass
vertical force
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This Chart We Observe That For Each Process There Is Driving
Force Called Energy On The Earth Surface Thermal Gradient Is Caused
By 1. Latitude 2.Seasons 3.Land And Water Distribution 4. Angle Of
Earhs Inclination The Densityof Natural Vegetation Is Greatly
Influenced By The Temperature And Precipitation Helps Indirectly
The Exogenic Processes. THE OTHER FACTORS OF CLIMATIC VARIATIONS
ARE1.Altitude 2. Angle Of Slope 3. Ocean Currents 4.Amount Of
Insolation Received By The Region 5. Wind Velocity And Direction 6.
Direcion Of The Slope 7. Amount And Kind Of Precipitation
8.Relation Between Precipitaion And Evaportion 9. Daily Rang Of
Temperature 10.Freezing And Thawing Frequency 11. Depth Of Frost
Penetration
The Sole Driving Force Behind All The Exogenic Process Is The
Sun
When Climatic Factors Are Common The Intensity Of Action Depend
On Type And Structure Of Rocks STRUCTURE INCLUDES folds,faults,
orientation inclination of beds, presence or absence of joints
,bedding planes hareness, softness of constituent minerals,
chemical susceptibility of mineral constituents , the permeability
or impermeability. Different types of rocks offer varying
resistances to various geomorphic processes . Particular rock may
be resistant to one process and non resistant to other process As a
result there is varied relief over the earth surface The effects of
exogenic forces may be small and slow but inlong run they have
greater effects Finally the surface of the earth is operated by
different geomorphic processes and at varying rates
WEATHERING: it is the acion of elements of weather on earth
materials
Weathering is defined as mechanical disintegration and chemical
deconposition of rocks through the actions of various element so
fweather and climate In weathering there is no motion of materials
takes place so it si in-situ or on site process
FACTORS INFLUENCING THE WEATHERING& DEPTH OF WEATHERING
1.GEOLOGICAL STRUCTURE 2.CLIMATE 3.TOPOGRAPHY 4. NATURAL
VEGETATION
THERE ARE THREE MAJOR GROUPS OF WEATHERING PROCESSES
(I) CHEMICAL (II) PHYSICAL/MECHANICAL (III)BIOLOGICAL WEATHERING
CHEMICAL WEATHERING PROCESSES Agroup of weathering processes viz;
solution , carnonation, hydration , oxidation and reduction asc on
the roks to decompose, dissolve orreduce them to a fine clastic
state through chemical reactions by oxygen ,surface /soil water and
other acids. Water and air along with heat must be present to speed
up all chemical reactions. Over and above the carbon dioxide
present in the air, decomposition of plants and animals increases
the quanitity of carbon dioxide underground . these chemical
reactions on various minerals are very much reactions on various
minerals are very much similar to the chemical reactions in a
laboratory.
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SOLUTION: the water /acid with dissolved content is called
solution. This process involves removal of solids in solution and
depends upon solubility of amineral in water or weak acids.when
water reacts with any solid many solids may become solution. Ex.
Sulphates, nitrates, potassium .
When rain comes these solids dissolve into solution with out
leaving any residue.
Calcium carbonate , magnesium bicorbanate present in the lime
stone are dissolved in and form
carbonic acid, produced by decaying organic matter along with
soil water greatly aids inthis reaction . Common salt is also
suceptible to this process.
CARBONATION: It is the reaction of carbonate and bicarbonate
with minerals such as feldspar, &
carboinate minerals from atmosphere and soil air is absorbed by
water to form carbonic
acid.Ca & Mg are dissolved in carbonic acid and washed away
to form the caves in lime stone region. Clay minerals are easily
eroded due to the presence of minerals which can exchange the ions
with the water . HYDRATION: it is the chemical addition of water .
minerals take up water and expand . this expansion increases the
volume of material.ex. calcium sulphate takes water and convert
into gypsum.it is unstabel than calcium sulphate.it is reversible
reaction and when this process continuous for longer time the
materials diintegrates. Many clayminerals swell and contract during
wetting and drying and a repetition of this process results in
cracking of overlying materials.salts inpore spaces undergo rapid
and repeated hydration and help in physical weathering through
exfoliation and granular disintegration OXIDATION AND REDUCTION
Oxidation means combination of minerals with oxygen to form oxides
and hydroxides. Oxidation occurs when there is sufficient water and
atmosphere. EX. Iron, manganes, sulphur, In the process of
oxidation breakdown occurs due the addition of oxygen.red colour of
iron becomes into yellow colour.when oxidised minerals re kept in
the places where there is no oxygen reduction takes place.ex. such
conditions occurs below water table waterlogged areas. Red colour
of iron becomes greenish or bluish grey.
PHYSICAL WEATHERING PROCESSES Factors Influencing The Physical
Weathering 1.Gravitational Force Overburden Pressure, Load And
Shearing Stress 2. Expansion Forces Due To Temperature Changes,
Crystal Growth Or Animal Activity 3.Water Pressures Controlled By
Wetting And Drying Cycles. They are mostly due to thermal
expansion, and pressure release. The repeated action of these
processes cause damage to the rocks UNLOADING AND EXPANSION:
Removal of overlying rock load because of continued erosion causes
vertical pressure release with the result that the upper layers of
the rock expand producing disintegration of rock masses.fractures
will develop parallel to the ground surface. In areas of curved
ground surface aarched fracaatures tend to produce massivce sheets
or exfoliation slabs of rock.exfoliation sheets resultinf from
expansion due to unloadinf and pressure release my measure hundreds
or even thousands of metres in horizontal extent.large
smooth rounded domes called exfoliation domes result due to this
process
TEMPERATURE CHANGES AND EXPANSION: Various minerals found in the
rocks expand at different rates when temperature increases. Each
one pushes others. When temperature falls contraction takes
place.because of diurnal changes in temperature the effects is
mostly on superficial layers of the rocks.the effects of this
process is significant in hot deserts and cold deserts.though it is
small the continuous process for longer time and larger area the
effect is greater. The effect is greater at the depth of the
rocks.fractures occurs parallel to the surface.due continuous
expansion and contraction the rock layers become lose and
exfoliation takes place.a large dome shaped structures are formed
due to this process. Tores which are large boulders also form due
this process.exfoliated domes are big insize where as
exfoliated
tores are varied sizes.
FREEZING THAWING AND FROST WEDGING:due to repeated freezing and
melting frost weathering occurs in the pores and cracks of rocks.it
is most effective in higher elevations of
the midlatitudes.
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Glacial areas are suhjected to frost wedging daily . In this
process the rate of freezing is more important. Rapid freezing
causes sudden expansion an dhigh pressure. Finally this process
makes the rock to break into pieces
SALT WEATHERING; salts in the rocks expand due to thermal action
hydration and crystallisation.ex. Calcium sodium magnesium
potassium and barium .high temperature between
30 to 50 of surface temperature indesertrs favour such salt
expansion.
Salt crystals in near surface porescause splitting of individual
grains within rocks,.which eventually fall off. This process of
falling off of individual grains may result in granualr
disingetrationor granular foliation.
Salt crystallisationis most effective of all salt weathering
processes, in areas with alternating wetting and drying conditions
salt crystal growth is favoured and the neighbouring grains are
pushed aside.sodium chloride and gypsum crystals in desert areas
heave up overlying layers of materials and with the result
polygonal cracks develop all over the heaved surface. With swalt
crystal growth, chalk breaks down most readily followed byLimstone
,Sandstone ,Chalk ,Gneiss
And Granite .
BIOLOGICAL WEATHERING: Removal or contribution of ions to the
environment due to biological activity is called biological
weathering.burrowing and wedging by organism like earthworks
tremites, rodents help in exposing the new surfaces to chemical
attack and assists in the pentration of moinsture and air..
SOME SPECIAL EFFECTS OF WEATHERING: Exfoliation is a is a result
but not a process . Removal of layers from curved surfaces result
into rounded surfaces.it occurs due to expansion and contraction
dnduced by temperature changes.exfoliation domes occur due to
unloading where
as tors occurs due to thermal expansion .
SIGNIFICANCE OF WEATHERING:Responsible for the formation of
soils and erosion and deposition. biodiversity is basically
depending on depth of weathering .erosion may not be significant
when there is no weathering.weathering aids mass wasting , erosion
and reduction of relief and changes in landforms .weathering of
rocks and depostion helps in the enrichment and concentrations of
certain
valuable ores of iron manganaese , aluminium copper.it is an
important process of soil formation.
ENRICHMENT:when rocks undergo weathering some materials are
removed through chemical or physical leaching by ground water and
thereby the concentrationof remaining materials increases. Without
such a weathering taking place , the concentration of the same
valuable material may not be sufficient and economically viable to
exploit , process and refine, this is what is called
enrichment.
MASS MOVEMENT: these movements transfer the mass of rock debris
down the slopes under the direct influence of gravity.air water ice
donot carry debris ,but debris carry them.the movements of
mass may range from slow to rapid.
TYPES OF MASS MOVEMENTS:creep,flow , slide and fall. mass
movements are active over weathered slopes than unwethered slopes.
mass movements are aided by gravity not any erosional agent. mass
movements do not come under erosion though there is shift of
material.
When force is greater than resistance mass movement occurs. Ex.
Weak unconsolidated material, thinly bedded rocks, faults, steeply
diffing beds, vertical cliffs ,steep slopes , abundant
prefipitation and torrential rains and scarcity of vegetation.
Activating causes precede mass movements: (i) removal of support
from below to materials above through natural or artificial
means
(ii)increase in gradient and height of slpes
(iii)overloading through additionof materials naturally or by
artificial filling
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(iv) overloading due to heavy rainfall saturation and
lubrication of slope materials
(v)removel of material or load from over the original slope
surfaces.
(vi) occurrence of earthquakes, explosions or macunery
(vii)excessive natural seepage
(viii)heavy draw down of water from lakes, reservoirs and
rivers
(ix)indiscriminate removal of natural vegetation
CLASSIFICATION OF MASS MOVEMENTS
Heave ,flow and slide are the three forms of movements the
relationship is shown in the figure no.
The mass movements can be grouped into three types
1.slow movements 2. Rapid movements 3. Land slide
SLOW MOVEMENTS
CREEP: It generally occurs on moderately steep, soil
covered slopes.
Movement of material is extremely slow. Material may
be rockdebris or soil
Ex. Bending of telephone pole,and fence poles.
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Types of creep : soil creep, talus creep rock creep rock glacier
creep
Solifluction:slow down slope flowing soil mass or fine grained
rock debris saturated or lubricated with water. It is common in
moist temperate areas where surface melting of deeply frozen
ground
and long continued rain respectively occur frequently.
MUD FLOW
RAPID MOVEMENTS
CONDITIONS: 1.humid climatic regions 2.gentle to steep slopes 3.
Heavy rain 4.
Loose soils
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EARTH FLOW: movements of water saturated clayey or silty erth
materials down low angle terraces or hillsides .
EARTHFLOW
In the absence of vegetation cover and with heavy rainfall,thick
layers of weathered materials get saturated with water and either
slowly or rapidly flow down along definite channels.it looks like a
channels of mud.when they overflow the channels they engulf the
roads and rail bridges.
They generally occur due to volcanic eruptions. Volcanic ash
dust and other fragments turn intomud due to heavy rains and flow
down as tougues or streams ofmud causing great
destruction to the human settlements.
DEBRIS AVALANCHES: Found in humid regions with or without
vegetationin narrow tracks of steep slopes. It is much faster than
mud flow, it is similar
to snow avalanches.
LANDSLIDES: these are rapid and perceptible movements.dry
materials are found .the size and shape of the materaials are
depending on the nature
of the rock,degree of weathering,steepness of slope.
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SLUMP:
slipping of one or several units of rock debris with a backward
rotationwith respect to the slope over which the movement takes
place
DEBRIS SLIDE:rapid rolling or sliding of earth debris without
backward rotation of mass is known as
debris slide.
Debris slide
ROCK FALL
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Rockslide sliding of individual rock masses down bedding joint
or fault surfaces . it generally occurs at the steep slopes.
Superficial layers of the rock gnerally fall.
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mass movement
Reasons for land slides along the Himalayas
1. Tectonically active 2. Made of sedimentary rocks 3. Steep
slopes 4. Heavy rains 5. Unconsolidated material is found
EROSION AND DEPOSITION Erosion involves acquisition and
transportation of rock debris Abration by rock debris carried by
geomorphic agents also aids erosion By erosion relief degrades .
the landscape is work down. Weatherin may not be pre condition for
erosion. Weathering , mass wasting, and erosion are degradational
processes. It is the erosion largly responsible for continuous
changes that the earth surface is undergoing. Erosion and
transportation are controlled by kinetic energy.wind running water
and glaciers are controlled by climate. Comparison of wind runing
water and glacier
wind Running water glacier
Predominent in hot deserts Found most parts of the earth Found
only in high latitude and altitude
Sand dunes are common features
Valleys and deltas are common features
U shaped valleys and morians are common
Ex. Sahara, atacama kalahari Amazon.Nile, Bramhaputra Greenland,
Antarctica
Air is gas Water is liquid Glacier is solid
Limited land forms Extensive land forms Limited land forms
High speed Normal speed Very slow movement
EROSION:application of kinetic energy associated with the agent
to the surface of the land
along which it moves. It is computed as KE = M=mass v= velocity
KE= kinetic energy SOIL FORMATION: Soil is the collection natural
bodies on the earths surface containing living matter and
supporting or cpable or suporting plants. Soil is a dynamic mateial
in which many chemical , bioligical , and physical activities go on
constantly. It is the result of decay, it is also a medium of
growth. It is changing and developing body. Characteristics are
changing from season to season. Too cold ,too hot , and dry areas
biological activity stops.organic matter increases when leaves fall
and decompose. PROCESS OF SOIL FORMATION: weathering is basic
process for soil formation. The weathered material is transported
and decomposed due to bacteria lichens and moss. The dead remains
increases the humus of the soil.minor grasses and ferns can grow.
Bushes , trees also grow .plants roots and burrowing animals help
the soil formation. PEDOLOGY:is Sceince of soil formation
PEDOLOGIST:is the scientist of soil formation
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SOIL FORMING FACTORS:1. Parent material 2. Topography 3. Climate
4. Biological activity. 5.time PARENT MATERIAL:passive control
factor ,it is insitu, onsite, or transported.it depends on texture,
structure, chemical compositon of the soil. Nature and depth of
weathering is an important factor.chemical composition ,texture are
the characteristics derived from patent material TOPOGRAPHY:passive
control factor,amount of exposer to the sun light,drainage
system,steep slopes have less deposition,gentle slopes have thick
soils. Plains have thick and dark coloured soils . In mid latitude
southern slopes expose to the sun light and get decomposed more .
CLIMATE:it is an active factor in soil formation. Climatic elements
are (i) moisture( interms of its intensity, frequency and
durationof precipitation evaporation and humidity
(II) Temperature in terms of seasonal and diurnal variation.
Precipitation increases the biological activity. Excess of water
helps to transport the dissolved particles to downward (eluviation)
Deposition of these particles is called Illuviation Heavy rainfall
removes the calcium , magnesium, sodium ,potasium along with
silica. Removal of silica is called desilication In dry areas
excess of evaporation leads to deposition of salts on the surface
of the soil These salt layers are called hard pans in the hot
deserts In tropical climates, under moderate rainfall conditions
calcium carbonate nodules are formed. Biological activity :plants
and animals add organic matter to the soil.also helps in
moisture
retention. Dead plants add humus to the soil In humid areas, the
bacterial activity is higher than cold areas
As a result undecomposed material is found in cold areas In hot
areas bacteria fix the nitrogen in the soil which is used by the
plants Rhizobium is the bacteria fix the nitrogen in the soil and
live in the roots of legumenace
plantsants, temites,rodents, earthworms change the chemical
composition of th soil. Time: Important controlling factor of soil
formatioon.Longer the time,thicker the soil layers. No
time limit for the formation of the soil layers.